1. Field
An aspect of the present invention relates to a pixel and an organic light emitting display, and more particularly, to a pixel capable of displaying an image with uniform brightness and an organic light emitting display using the same.
2. Description of the Related Art
Recently, various flat panel displays (FPD) having reduced weight and volume as compared to cathode ray tubes (CRT) have been developed. The FPDs include liquid crystal displays (LCD), field emission displays (FED), plasma display panels (PDP), and organic light emitting displays.
Among the FPDs, the organic light emitting displays display images using organic light emitting diodes (OLED) that generate light by re-combination of electrons and holes. The organic light emitting display has high response speed and is driven with low power consumption.
FIG. 1 is a circuit diagram illustrating a pixel of a conventional organic light emitting display. Referring to FIG. 1, a pixel 4 of the conventional organic light emitting display includes an organic light emitting diode OLED and a pixel circuit 2 coupled to a data line Dm and a scan line Sn to control the OLED.
The anode electrode of the OLED is coupled to the pixel circuit 2 and the cathode electrode of the OLED is coupled to a second power source ELVSS. The OLED emits light with the brightness corresponding to the current supplied from the pixel circuit 2.
The pixel circuit 2 controls the amount of current supplied to the OLED to correspond to a data signal supplied to the data line Dm when a scan signal is supplied to the scan line Sn. Therefore, the pixel circuit 2 includes a second transistor M2 coupled between a first power source ELVDD and the OLED, a first transistor M1 coupled between the second transistor M2, the data line Dm, and the scan line Sn, and a storage capacitor Cst coupled between the gate electrode and the first electrode of the second transistor M2.
The gate electrode of the first transistor M1 is coupled to the scan line Sn and the first electrode of the first transistor M1 is coupled to the data line Dm. The second electrode of the first transistor M1 is coupled to one terminal of the storage capacitor Cst. Here, the first electrode is set as one of a source electrode and a drain electrode and the second electrode is set as an electrode different from the first electrode. For example, when the first electrode is set as the source electrode, the second electrode is set as the drain electrode. The first transistor M1 coupled to the scan line Sn and the data line Dm is turned on when the scan signal is supplied from the scan line Sn to the gate electrode of the first transistor M1 to supply the data signal supplied from the data line Dm to the storage capacitor Cst. At this time, the storage capacitor Cst charges with the voltage corresponding to the data signal.
The gate electrode of the second transistor M2 is coupled to one end of the storage capacitor Cst and the first electrode of the second transistor M2 is coupled to the other terminal of the storage capacitor Cst and the first power source ELVDD. The second electrode of the second transistor M2 is connected to the anode electrode of the OLED. The second transistor M2 controls the amount of current that flows from the first power source ELVDD to the second power source ELVSS via the OLED to correspond to the value of the voltage stored in the storage capacitor Cst. At this time, the OLED emits the light corresponding to the amount of current supplied from the second transistor M2.
However, the pixel 4 of the conventional organic light emitting display cannot display an image with uniform brightness. In detail, the threshold voltage of the second transistor M2 (a driving transistor) included in the pixel 4 is set to vary with the pixel 4 due to process deviation. When the threshold voltage of the driving transistor is set to vary, although data signals corresponding to the same gray level are supplied to the plurality of pixels 4, light components with different brightness components are generated due to a difference in the threshold voltage of the driving transistor.
In order to solve the above and/or other problems, a structure of additionally forming transistors in the pixels 4 is suggested in order to compensate for the threshold voltage of the driving transistor. For example, in the Korean Patent Publication No. 2007-0083072, the threshold voltage of the driving transistor is compensated for using the six transistors included in each of the pixels 4.
However, in the Korean Patent Publication No. 2007-0083072, since one pixel is coupled to a plurality of wiring lines Sn, Sn−1, En, Vint, and Dm, complexity of a process increases and reliability deteriorates.